Formation of spores by species of Bacillus and Clostridium is a primitive system of cell differentiation. It involves an asymmetrically located division. This gives rise to two distinct cell types, the mother cell and the prespore, which have radically different developmental fates. The prespore is engulfed by the mother cell and develops into the mature, heat- resistant spore. The mother cell is required for that development but ultimately lyses. In Bacillus subtilis it has been shown that two RNA polymerase sigma factors, F and E, are activated upon division, with sigmaF active exclusively in the prespore and sigmaE active exclusively in the mother cell. These sigma factors direct the subsequent program of compartmentalized gene expression, but do not direct the process of compartmentalization. The main problems being addressed are how compartmentalization of gene expression is established and how gene expression is coordinated with morphological changes. A dominant feature in the thinking about compartmentalization in Bacilli and Clostridia has been the grossly asymmetric location of the sporulation division. It is proposed to test for other possible determinants of compartmentalization in a species of spore-forming coccus, Sporosarcina ureae, in which the sporulation division is symmetrically located. It is proposed to develop a two-part system that tests the completeness of compartmentalization. This system will be used to search for and characterize B. subtilis mutants with impaired compartmentalization. It will also be used to test the completeness of compartmentalization in S. ureae. It is proposed to explore the requirement for the SpoIIE protein in order to have an asymmetric division in B. subtilis. It is proposed to test the role of chromosome resolution in spore formation. It is proposed to identify and characterize genes involved in engulfment of the prespore by the mother cell in B. subtilis.